Objective. This study estimates the relationship between firearms availability and homicides in 150 countries. More specifically, this study compares the predictive validity of three different firearms availability indicators: (1) the percentage of homes owning a firearms; (2) the percentage of persons carrying a firearm; and (3) the rate of firearms per 100 populations. Carrying a firearm is conceptualized as a central dimension of a self-defense culture and it should display a stronger association with homicides than the two other indicators. Methodology. Data comes from the Enquête Mondiale sur l’Homicide, Small Arms Survey and other publications from the United Nations. Descriptive, bivariate and multivariate analyses were conducted to assess the relationship between firearms and homicides. Results. Results show that, in general, the percentage of persons carrying firearms is positively associated with the homicide rate and the proportion of homicides committed with a firearm. Economic inequalities and corruption within the criminal justice system are both positively associated with homicides. Conclusion. Results do not support the self-defense thesis. Conversely, firearm carrying is associated with high homicide rates, which is in keeping with studies showing that a firearm is the perfect crime facilitator. Hence, technologies developed by forensic and information sciences represent promising avenues to track firearms transactions and support criminal investigations.